I recall your post but don't remember the details so excuse me if I go over anything already said.
Firstly, quoting from another post of mine
If a prime-focus dish and off-set dish have the same F/D ratio then, by the laws of physics, they will have the same gain. There will be a slight advantage to the off-set as the LNB and arm won't be shading the dish but otherwise they will be the same.
The thing is that they generally aren't the same. The deeper a dish is, the lower is its gain. Why would anyone not want a dish to have as much gain as possible? Well, the problem is that a shallow (high gain) dish has poorer rejection of unwanted signals from the side compared to a deep dish and sometimes it's more important to reject the interference.
The F/D ratio is the distance from the LNB to the centre of the dish and D is the diameter of the dish. Obviously this is relatively easy to work out for a prime focus dish (circular) and less so for an off-set but the point is that they are different, which is what Channel Hopper was alluding to in his post - even if you can you physically fit the same LNB and feed horn to each typoe of dish they are matched for different F/D ratios and will not collect the correct amount of signal.
Moving on to an elliptical dish, these are a type of off-set dish. These first came about in the UK when $ly went digital using Astra 2 with its higher power transmitters. As the signal is stronger you can use a smaller dish to collect the signal but as the dish gets smaller angle of acceptance increases. Generally speaking satellites are spaced about 3 degrees apart which gives enough room for 60cm, and larger, dishes to reject the signals from neighbouring satellites. When you come doen to 45cm or so the dish can, even though it's pointing accurately at one satellite, inadvertantly collect some signal from a neighbour and this can cause interference. The solution is to widen the dish at the sides, to reject the neighbours, but keep the height reduction. The result is that the dish looks smaller and neater but still does its job. This was a major consideration for $ly who were combatting accusations of "dish blight"
Even though an elliptical dish has the same F/D ratio as other off-set dishes it still needs a special LNB (or, more properly, LNBF) because the feedhorn is part of the LNB. The special LNBF is shaped to match the elliptical dish and provide effective rejection of interference whilst collecting as much signal as possible.
Does that make it any clearer or have I just confused things further?
